Method and apparatus for using control channel format indicator (CCFI) codewords in a wireless communication system

ABSTRACT

A method of transmitting a control channel format indicator (CCFI), also known as PCFICH (Physical Control Format Indicator Channel), in case where the length of a coded CCFI is not an integer multiple of three, including mapping a plurality of two-bit CCFI into a codebook with each component codeword having three bits; generating a sequence of codewords selected from the codebook by repeating the selected component codeword for predetermined times; generating a codeword by concatenating the sequence of the selected component codewords with the original CCFI bits; and transmitting the codeword carrying information of CCFI. The method further includes a step of generating a permutation of each of the four codewords by assigning K repetitions of the three-bit component codeword to the number of K resource units respectively and mapping remaining K bits of each of the four codewords separately to the number of K resource units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/213,012 filed on Jun. 12, 2008 now U.S. Pat. No. 8,094,747, entitled“TRANSMIT METHODS FOR CCFI/PCFICH IN A WIRELESS COMMUNICATION SYSTEM,”which claims priority to U.S. Provisional Patent Application No.60/929,869 filed on Jul. 16, 2007, and U.S. Provisional PatentApplication No. 60/929,791 filed on Jul. 12, 2007. U.S. patentapplication Ser. No. 12/213,012 is assigned to the assignee of thepresent application and is incorporated by reference into thisdisclosure as if fully set forth herein. This disclosure hereby claimspriority under 35 U.S.C. §120 to U.S. patent application Ser. No.12/213,012.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from applicationsearlier filed in the U.S. Patent & Trademark Office on 12 Jul. 2007 andthere duly assigned Ser. No. 60/929,791, and on 16 Jul. 2007 and thereduly assigned Ser. No. 60/929,869, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for coding aCCFI (Control Channel Format Indicator) channel, also known as PCFICH(Physical Control Format Indicator Channel), and more particularly, to amethod and apparatus for coding a CCFI channel using a concatenation ofrepeated (3,2) codewords and original CCFI bits, for the case where atotal result coded length of CCFI is not an integer multiple of three.

2. Description of the Related Art

Three references of the present invention are listed as below.

-   [1]. 3GPP RAN WG1#48bis Chairman's Notes, March 2007, Malta.-   [2]. R1-050271, “Evaluation of Diversity in Evolved UTRA”, Samsung,    RAN1#40bis, Beijing China, April 2005.-   [3]. “Transmit Diversity for Acknowledgement and Category 0 bits in    a Wireless communication System”, earlier filed provisional in the    U.S. Patent & Trademark Office on 26 Apr., 2007 and there duly    assigned Ser. No. 60/924,020 and earlier filed provisional in the    U.S. Patent & Trademark Office on 9 May, 2007 and there duly    assigned Ser. No. 60/924,339.

Reference [3] discusses several approaches of coding and transmitdiversity for both the Category 0 bits and ACK/NACK channels.

Orthogonal Frequency Division Multiplexing (OFDM) is a technology tomultiplex data in frequency domain. Modulation symbols are carried onfrequency sub-carriers. The total bandwidth in an OFDM system is dividedinto narrowband frequency units called subcarriers. The number ofsubcarriers is equal to the FFT/IFFT size N used in the system. Ingeneral, the number of subcarriers used for data is less than N becausesome of the subcarriers located at the edge of the frequency spectrumare reserved as guard subcarriers. In general, no information may betransmitted on guard subcarriers.

A typical cellular radio system includes a collection of fixed basestations (BS) that define a radio coverage area or a cell. Typically, anon-line-of-sight (NLOS) radio propagation path exists between a basestation and a mobile station due to natural and man-made objects thatare situated between the base station and the mobile station. As aconsequence, the radio waves propagate via reflections, diffractions andscattering. The arriving waves at the mobile station (MS) in thedownlink direction (at the BS in the uplink direction) experienceconstructive and destructive additions because of different phases ofthe individual waves. This is due the fact that, at high carrierfrequencies typically used in the cellular wireless communication, smallchanges in the differential propagation delays introduces large changesin the phases of the individual waves. When the MS is moving or changesoccur in the scattering environment, the spatial variations in theamplitude and phase of the composite received signal will manifestthemselves as the time variations known as Rayleigh fading or fastfading. The time-varying nature of the wireless channel requires veryhigh signal-to-noise ratio (SNR) in order to provide desired bit erroror packet error reliability.

Diversity is widely used to combat the effect of fast fading. The ideais to provide the receiver with multiple faded replicas of the sameinformation-bearing signal. On the assumption of independent fading ofeach of the antenna branches, the probability that the instantaneous SNRis below a certain threshold on each branch is approximately p^(L) wherep is the probability that the instantaneous SNR is below the certainthreshold on each antenna branch.

The methods of diversity generally fall into the following categories:space, angle, polarization, field, frequency, time and multipathdiversity. Space diversity may be achieved by using multiple transmit orreceive antennas. The spatial separation between the multiple antennasis chosen so that the diversity branches experience fading with littleor no correlation. Transmit diversity uses multiple transmit antennas inorder to provide the receiver with multiple uncorrelated replicas of thesame signal. Transmit diversity schemes may further be divided into openloop transmit diversity and closed-loop transmit diversity schemes. Inan open loop transmit diversity approach, no feedback is required fromthe receiver. In a known arrangement of a closed loop transmitdiversity, the receiver computes the phase and amplitude adjustment thatshould be applied at the transmitter antennas to maximize the receivedsignal power at the receiver. In another arrangement of the closed looptransmit diversity referred to as selection transmit diversity (STD),the receiver provides feedback information to the transmitter onantenna(s) to be used for transmission.

Dynamic Category 0 (Cat 0) bits are a LTE terminology used in 3GPP LTEstandard body. The role of Cat0 is to support dimensioning (scaling) ofthe downlink control channel by indicating the number of downlink anduplink scheduling grants. The current working assumption in reference[1] is that the dynamic Cat0 bits have a maximum size of two bits, andthe dynamic Cat0 bits should be transmitted once during every subframewhere a control channel element (CCE) is present. The informationconveyed by Cat0 bits includes, but not limited to, the number of OFDMsymbols used for all control channels in the subframe. The transmitdiversity of the Cat0 bits is not finalized, and it is the objective ofthe present invention to provide a simple and efficient transmitdiversity scheme that captures both spatial and frequency diversity inthe channel. In reference [3], several approaches of coding and transmitdiversity have been described for both the Category 0 bits and ACK/NACKchannels. In the 3GPP standard RAN1 meeting in May 2007, the Category 0bits have been renamed as CCFI (Control Channel Format Indicator). Inthe present invention, one additional coding method is proposed, as wellas frequency domain resource mapping methods for the transmission ofCCFI channel.

In addition, it was proposed in reference [3] to use a (3,2,2) binarylinear code to map the 2 Cat1 bits into a 3-bit codeword c₁c₂c₃, andthis codeword belongs to a codebook of size four with a minimum Hammingdistance two between any pairs of codewords. One example of the (3,2)codebook in reference [3] is c₁c₂c₃εC₁={111, 100, 010 001}.

Because the size of (3,2) codebook as above presented is three, merelyrepeating the 3-bit codeword may only be suitable for a case where thelength of a coded CCFI is an integer multiple of three. Therefore, it isimportant to provide a CCFI coding method in a case where the length ofa coded CCFI is not an integer multiple of three.

SUMMARY OF THE INVENTION

It is therefore one object of the present invention to provide animproved process and apparatus for solving the above mentioned problems.

It is another object of the present invention to provide a CCFI codingmethod in a case where the length of a coded CCFI is not an integermultiple of three.

In one embodiment of the present invention, it is proposed to code theCCFI channel using a concatenation of repeated (3,2) codewords anduncoded CCFI bits, for the case where the total codeword length is notan integer multiple of three. Because the size of the (3,2) codebook asabove presented is three and thus it is important to provide a CCFIcoding method in a case where the length of a coded CCFI is not aninteger multiple of three.

As shown in the table below, a mapping between the two bits CCFI and thecomponent codewords in a (3,2) codebook is established.

CCFI bits Component codeword c₁c₂c₃ Component codeword c₁c₂c₃ b₁b₂(assuming (3, 2) codebook C₂) (assuming (3, 2) codebook C₁) 00 000 11101 011 100 10 101 010 11 110 001

The length-32 codewords are generated in the following procedures.

(1) A length-3 component codeword c₁c₂c₃ is generated as shown in Tableabove;

(2) the component codeword c₁c₂c₃ is repeated ten times to generate alength-30 sequence; and

(3) the length-30 sequence is concatenated with the original CCFI bitsb₁b₂.

The resulting four codewords of codebook A corresponding to eachcodeword of codebook C₂ are:

000 000 000 000 000 000 000 000 000 000 00 (cw1)

011 011 011 011 011 011 011 011 011 011 01 (cw 2)

101 101 101 101 101 101 101 101 101 101 10 (cw 3)

110 110 110 110 110 110 110 110 110 110 11 (cw 4)

Codebook A

In another embodiment of the current invention, when the CCFI has onlythree states (i.e., CCFI is any three of “00”, “01”, “10” and “11”),then any of the three codewords in the above set may be used to carrythe CCFI information.

In another embodiment of the present invention, the codebook generatedabove is column-wise permuted in order to fit the K 1×2 RU resourceconfiguration, which has a total of 4K coded bits. In this permutationmethod, based on the sequential concatenation of the repeated codewords,K repetitions of 3-bit component codeword are assigned to the K RUs(leaving one bit open at each RU), and then the remaining K bits aremapped separately to the K RUs. Other codewords of codebook A maydeviate in the same method. The resulting codebook deviated fromcodebook A is called Codebook B as shown below. The codebook B may bebetter than codebook A in fading channels, since a full repetition to anRU is mapped as much as possible.

0000 0000 0000 0000 0000 0000 0000 0000 (cw1)

0110 0111 0111 0110 0111 0111 0110 0111 (cw 2)

1011 1010 1011 1011 1010 1011 1011 1010 (cw 3)

1101 1101 1100 1101 1101 1100 1101 1101 (cw 4)

Codebook B

In another embodiment of the current invention, a variation of thecodebook A may obtained by mapping the CCFI bits to codebook C1, insteadof codebook C2. The same repetition and concatenation used in generatingthis new codebook, called codebook C.

111 111 111 111 111 111 111 111 111 111 00 (cw1)

100 100 100 100 100 100 100 100 100 100 01 (cw 2)

010 010 010 010 010 010 010 010 010 010 10 (cw 3)

001 001 001 001 001 001 001 001 001 001 11 (cw 4)

Codebook C

In another embodiment of the current invention, same column-wisepermutation as stated above is applied to Codebook C in order togenerate Codebook D.

1111 1111 1111 1111 1111 1111 1110 1110 (cw1)

1001 1000 1000 1001 1000 1000 1000 1001 (cw 2)

0100 0101 0100 0100 0101 0100 0101 0100 (cw 3)

0010 0010 0011 0010 0010 0011 0011 0011 (cw 4)

Codebook D

In another embodiment of the current invention, when the CCFI has onlythree states, any three codewords in a given codebook (e.g, Codebook A,B, C, D, etc) may be used to carry the CCFI information.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is an illustration of an Orthogonal Frequency DivisionMultiplexing (OFDM) transceiver chain having transmitter chain andreceiver chain;

FIG. 2 shows an Alamouti 2×1 space-time diversity scheme;

FIG. 3 shows an Alamouti 2×1 space-frequency scheme;

FIG. 4 shows an example of a method of a column-wise permutation; and

FIGS. 5A and 5B are flowcharts illustrating procedural steps oftransmitting and receiving CCFI according to different embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Three references of the present invention are listed as below.

-   [1]. 3GPP RAN WG1#48bis Chairman's Notes, March 2007, Malta-   [2]. R1-050271, “Evaluation of Diversity in Evolved UTRA”, Samsung,    RAN1#40bis, Beijing China, April 2005-   [3]. “Transmit Diversity for Acknowledgement and Category 0 bits in    a Wireless communication System”, earlier filed provisional in the    U.S. Patent & Trademark Office on 26 Apr., 2007 and there duly    assigned Ser. No. 60/924,020 and earlier filed provisional in the    U.S. Patent & Trademark Office on 9 May, 2007 and there duly    assigned Ser. No. 60/924,339.

In reference [3], several approaches of coding and transmit diversityare described for both the Category 0 bits and ACK/NACK channels. In the3GPP standard RAN1 meeting in May 2007, the Category 0 bits have beenrenamed as CCFI (Control Channel Format Indicator). In the practice ofthe principle of the present invention, a few additional coding methodsas well as frequency domain resource mapping methods for thetransmission of CCFI channel are disclosed. Here, the CCFI is also knownas PCFICH (Physical Control Format Indicator Channel).

Orthogonal Frequency Division Multiplexing (OFDM) is a technology tomultiplex data in frequency domain. Modulation symbols are carried onfrequency sub-carriers. FIG. 1 illustrate of an Orthogonal FrequencyDivision Multiplexing (OFDM) transceiver chain having a transmitterchain and a receiver chain. A sample of Orthogonal Frequency DivisionMultiplexing (OFDM) transceiver chain is shown in FIG. 1. At atransmitter chain 100, control signals or data signals are modulated bya modulator 101 and the modulated signals are serial-to-parallelconverted by a serial-to-parallel convertor 112. An Inverse Fast FourierTransform (IFFT) unit 114 is used to transfer the modulated signal ordata from frequency domain to time domain, and the modulated signalstransferred to the time domain is parallel-to-serial converted by aparallel-to-serial convertor 116. A cyclic prefix (CP) or zero prefix(ZP) is added to each OFDM symbol at a CP insertion stage 118 to avoidor alternatively, to mitigate the impact due to multipath fading at amultipath fading channel 122. Signals from cyclic prefix (CP) insertionstage 118 are applied to transmitter front end processing unit 120, RFamplifier 121 and then single or multiple antennas 123. Therefore, thesignals transmitted by transmitter chain 100 are received by receiverchain 140. At a receiver chain 140, assuming that perfect time andfrequency synchronization are achieved, signals received by receivingsingle or multiple antennas 125 is applied to receiver front endprocessing unit 124, are processed at a cyclic prefix (CP) removal stage126 which removes the cyclic prefix (CP) of the received signal. Signalsprocessed in cyclic prefix (CP) removal stage 126 are furtherserial-to-parallel converted by a serial-to-parallel convertor 128. AFast Fourier Transform (FFT) unit 130 transfers the received signalsfrom the time domain to the frequency domain for further processing,including parallel-to-serial conversion by a parallel-to-serialconvertor 132 and being demodulation by signal de-modulator 134.

The total bandwidth in an OFDM system is divided into narrowbandfrequency units called subcarriers. The number of subcarriers is equalto the FFT/IFFT size N used in the system. In general, the number ofsubcarriers used for data is less than N because some of the subcarrierslocated at the edge of the frequency spectrum are reserved as guardsubcarriers. As a general rule, no information may be transmitted onguard subcarriers.

A typical cellular radio system includes a collection of fixed basestations (BS) that define a radio coverage area or a cell. Typically, anon-line-of-sight (NLOS) radio propagation path exists between a basestation and a mobile station due to natural and man-made objects thatare situated between the base station and the mobile station. As aconsequence, the radio waves propagate via reflections, diffractions andscattering. The arriving waves at the mobile station (MS) in thedownlink direction (at the BS in the uplink direction) experienceconstructive and destructive additions because of different phases ofthe individual waves. This is due the fact that, at the high carrierfrequencies typically used in the cellular wireless communication, smallchanges in the differential propagation delays introduce large changesin the phases of the to individual waves. Additionally, when the MS ismoving or changes occur in the scattering environment, the spatialvariations in the amplitude and phase of the composite received signalwill manifest themselves as the time variations known as Rayleigh fadingor fast fading. The time-varying nature of the wireless channel requiresvery high signal-to-noise ratio (SNR) in order to provide desired biterror or packet error reliability.

Diversity is widely used to combat the effects of fast fading. The ideais to provide the receiver with multiple faded replicas of the sameinformation-bearing signal. On the assumption of independent fading ofthe signals broadcast by each of the antenna branches, the probability,that the instantaneous SNR is below a certain threshold on each branchis approximately p^(L), where p is the probability that theinstantaneous SNR is below the certain threshold on each antenna branch.L is the number of antenna branches. From a system operation viewpoint,“antenna branch” is also known as “antenna ports”, and it indicates thenumber of antennas at the base station.

The methods of diversity that are suitable for use fall into thefollowing categories: space, angle, polarization, field, frequency, timeand multipath diversity. Space diversity may be achieved by usingmultiple transmit or receive antennas. The spatial separation betweenthe multiple antennas is chosen so that the diversity branchesexperience fading with little or no correlation of the signals duringthe transit between the transmitting and receiving antennas. Transmitdiversity uses multiple transmitting antennas in order to provide thereceiver with multiple uncorrelated replicas of the same signal.Transmit diversity schemes may further be divided into open looptransmit diversity and closed-loop transmit diversity schemes. In anopen loop transmit diversity approach, no feedback is required from thereceiver. In one known arrangement of a closed loop transmit diversity,the receiver computes the phase and amplitude adjustment that should beapplied at the transmitter antennas to maximize the received signalpower at the receiver. In another arrangement of the closed looptransmit diversity referred to as selection transmit diversity (STD),the receiver provides feedback information to the transmitter onantenna(s) to be used for transmission.

An example of open-loop transmit diversity scheme is the Alamouti 2×1space-time diversity scheme. FIG. 2 shows an Alamouti 2×1 space-timediversity scheme. In this approach during any symbol period, two datasymbols are transmitted simultaneously from the two transmit antennasANT1 and ANT2. Suppose during the first symbol interval t1, the symbolstransmitted from ANT1 and ANT2 are denoted as S₁ and S₂ respectively asshown in FIG. 2. During the next symbol period, the symbols transmittedfrom ANT1 and ANT2 are −S₂* and S₁* respectively where x* represents thecomplex conjugate of x. With certain processing at the receiver,original symbols S₁ and S₂ may be recovered. Here, the instantaneouschannel gain estimates h1 and h2 on ANT 1 and ANT 2, respectively, arerequired for faithful recovery at the receiver. This requires separatepilot symbols on both of the antennas in order to provide channel gainestimation at the receiver. The diversity gain achieved by Alamouticoding is the same as that which may be achieved in Maximum RatioCombining (MRC).

A 2×1 Alamouti scheme may also be implemented in a space-frequency codedform. FIG. 3 shows a 2×1 Alamouti scheme implemented in aspace-frequency coded form. In this case, the two symbols are sent ontwo different frequencies, i.e., subcarriers f1 and f2, for example, ondifferent subcarriers in an Orthogonal Frequency Division Multiplexing(OFDM) system as shown in FIG. 3. When implemented in a space-frequencycoded form in the open-loop transmit diversity scheme, the 2×1 Alamoutispace-frequency diversity scheme illustrated by FIG. 3 shows an Alamouti2×1 space-frequency diversity scheme in which during any symbol period,two data symbols are transmitted simultaneously from the two transmitantennas ANT1 and ANT2. If during the first frequency f1, the symbolstransmitted from ANT1 and ANT2 are denoted as S₁ and S₂ respectively asshown in FIG. 3. During the next symbol period, the symbols transmittedfrom ANT1 and ANT2 are −S₂* and S₁* respectively where x* represents thecomplex conjugate of x. Original symbols S₁ and S₂ may be recovered bythe receiver. Here, the instantaneous channel gain estimates h1 and h2on ANT 1 and ANT 2, respectively, are required for faithful recovery atthe receiver. This requires separate pilot symbols on both of theantennas in order to provide channel gain estimation at the receiver.The diversity gain achieved by Alamouti coding is the same as that whichmay be achieved in Maximum Ratio Combining (MRC).

The received signals r₁ and r₂ at the mobile station in subcarrier f1,r1, and in subcarrier f2, r2, may be written as:r ₁ =h ₁ s ₁ +h ₂ s ₂ +n ₁r ₂ =h ₁ s ₂ *+h ₂ s ₁ *+n ₂  (1)where h1 and h2 are channel gains from ANT1 and ANT2 respectively. Theassumption here is that the channel from a given antenna does not changebetween subcarriers f1 and f2. The mobile station performs equalizationon the received signals and combines the two received signals (r1 andr2) in order to recover the symbols S1 and S2.

$\begin{matrix}{\begin{matrix}{{\hat{s}}_{1} = {{h_{1}^{*}r_{1}} + {h_{2}r_{2}^{*}}}} \\{= {{h_{1}^{*}\left( {{h_{1}s_{1}} + {h_{2}s_{2}} + n_{1}} \right)} + {h_{2}\left( {{{- h_{1}}s_{2}^{*}} + {h_{2}s_{1}^{*}} + n_{2}} \right)}^{*}}} \\{= {{\left( {{h_{1}}^{2} + {h_{2}}^{2}} \right)s_{1}} + {h_{1}^{*}n_{1}} + {h_{2}n_{2}^{*}}}}\end{matrix}\begin{matrix}{{\hat{s}}_{2} = {{h_{2}^{*}r_{1}} + {h_{1}r_{2}^{*}}}} \\{= {{h_{2}^{*}\left( {{h_{1}s_{1}} + {h_{2}s_{2}} + n_{1}} \right)} + {h_{1}\left( {{{- h_{1}}s_{2}^{*}} + {h_{2}s_{1}^{*}} + n_{2}} \right)}^{*}}} \\{= {{\left( {{h_{1}}^{2} + {h_{2}}^{2}} \right)s_{2}} + {h_{2}^{*}n_{1}} + {h_{1}n_{2}^{*}}}}\end{matrix}} & (2)\end{matrix}$It may be seen that both the transmitted symbols S1 and S2 achieve fullspatial diversity.

The term Dynamic Category 0 (Cat 0) bits is a LTE terminology used bythe 3GPP LTE standard body. The role of Cat0 is to support dimensioning(scaling) of the downlink control channel by indicating the number ofdownlink and uplink scheduling grants. The current working assumption inreference [1] is that the dynamic Cat1 bits have a maximum size of twobits, and should be transmitted during every subframe where a controlchannel element (CCE) is present. The information conveyed by Cat1 bitsincludes, but is not limited to, the number of OFDM symbols used for allcontrol channels in the subframe. The transmit diversity of the Cat1bits is not finalized, and it is one of the objectives of the presentinvention to provide a simple and efficient transmission and receptiondiversity scheme that is enable to capture both spatial and frequencydiversity in the channel. In reference [3], several approaches of codingand transmit diversity have been described for both the Category 0 bitsand ACK/NACK channels. In the 3GPP standard RAN1 meeting in May 2007,the Category 0 bits have been renamed as CCFI (Control Channel FormatIndicator). In the present invention, one additional coding method isproposed, as well as frequency domain resource mapping methods for thetransmission of CCFI channel.

In addition, it was proposed in reference [3] to use a (3,2,2) binarylinear code to map the two Cat1 bits into a 3-bit codeword c₁c₂c₃, andto assign this codeword belongs to a codebook of size four with aminimum Hamming distance two between any pairs of codewords. A linearcode (n,k,d) means a code with each codeword length of n coded bits, andeach codeword correspond to a message with length k information bits.The minimum hamming distance of the codebook is d. Once the 3-bitcodeword is specified, it will be repeated and rate-matched to fit the2K channel symbols that are going to be used for the Cat1 bits. A (3,2)codebook is a short-hand notation of (3,2,2) code. One example of the(3,2) codebook in reference [3] is c₁c₂c₃εC₁={111, 100, 010 001}.

In one embodiment of the present invention, it is proposed to code theCCFI channel using a concatenation of repeated (3,2) codewords anduncoded CCFI bits, for the case where the total codeword length is notan integer multiple of three. Because the size of (3,2) codebook asabove presented is three and thus it is important to provide a CCFIcoding method in a case where the length of a coded CCFI is not aninteger multiple of three.

For example, when a total number of K 1×2 resource units (RU) areassigned to the CCFI channel, there are 2K channel symbols and 4Kchannel bits, assuming QPSK modulation on each channel symbol. Here, 1×2RU occupies one OFDM symbol and two neighboring subcarriers. Forexample, when K=8 RUs, there are 2K=16 channel symbols and 32 codedbits. 32 is not an integer multiple of three.

As shown in Table 1, a mapping between the 2 bits CCFI and the componentcodewords in a (3,2) codebook is established. Table 1 is a mappingbetween CCFI bits and component codewords as shown above. Here, the(3,2) codebook is c₁c₂c₃εC₂={000, 011, 101, 110}. Note the above shown(3,2) codebook is equivalent to c₁c₂c₃εC₁={111, 100, 010 001}. CCFI bitsb₁ and b₂ are original CCFI bits. Component codewords of two (3,2)codebooks C₁ and C₂ corresponding to each state of CCFI bits are shownin Table 1.

TABLE 1 Mapping between CCFI bits and component codewords. CCFI bitsComponent codeword c₁c₂c₃ Component codeword c₁c₂c₃ b₁b₂ (assuming (3,2) codebook C₂) (assuming (3, 2) codebook C₁) 00 000 111 01 011 100 10101 010 11 110 001

Four codewords with length of 32 generated for the CCFI bits b₁b₂ areshown as follows, for the example above. Here, (3,2) codebook C₂ areused. The length-32 codewords are generated by modulator 101 with thefollowing procedural steps.

(1) A length-3 component codeword c₁c₂c₃ is generated as shown in Table1;

(2) the component codeword c₁c₂c₃ is repeated ten times to generate alength 30 sequence; and

(3) the length-30 sequence is concatenated with the original CCFI bitsb₁b₂.

Here, the codeword c₁c₂c₃ is repeated └4K/3┘ times, and the resultingsequence is concatenated with the original CCFI bits b₁b₂. Thisconcatenated bit sequence is the final channel bit sequence to bemodulated and mapped into channel symbol.

The resulting four codewords of codebook A corresponding to eachcodeword of codebook C₂ are:

000 000 000 000 000 000 000 000 000 000 00 (cw1)

011 011 011 011 011 011 011 011 011 011 01 (cw 2)

101 101 101 101 101 101 101 101 101 101 10 (cw 3)

110 110 110 110 110 110 110 110 110 110 11 (cw 4)

Codebook A

In another embodiment of the current invention, if the CCFI has onlythree states (i.e., CCFI is any three of “00”, “01”, “10” and “11”),then any of the 3 codewords in the above set may be used to carry theCCFI information.

In another embodiment of the present invention, the codebook generatedabove is column-wise permuted to fit the K 1×2 RU resourceconfiguration, which has a total of 4K coded bits. FIG. 4 shows anexample of a method of a column-wise permutation. In this permutationmethod, based on the sequential concatenation of the repeated codewords,K repetitions of 3-bit component codeword are assigned to the K RUs(leaving one bit open at each RU), and then the remaining K bits aremapped separately to the K RUs. The permutation of CW4 is illustrated inFIG. 4. Other codewords of codebook A may be deviated in the samemethod. The resulting codebook deviated from codebook A is calledCodebook B as shown below. The codebook B may be better than codebook Ain fading channels, since a full repetition to an RU is mapped as muchas possible.

0000 0000 0000 0000 0000 0000 0000 0000 (cw1)

0110 0111 0111 0110 0111 0111 0110 0111 (cw 2)

1011 1010 1011 1011 1010 1011 1011 1010 (cw 3)

1101 1101 1100 1101 1101 1100 1101 1101 (cw 4)

Codebook B

In another embodiment of the current invention, a variation of thecodebook A may obtained by mapping the CCFI bits to codebook C1, insteadof codebook C2, as shown in Table 1. The same repetition andconcatenation used in generating this new codebook, called codebook C.

111 111 111 111 111 111 111 111 111 111 00 (cw1)

100 100 100 100 100 100 100 100 100 100 01 (cw 2)

010 010 010 010 010 010 010 010 010 010 10 (cw 3)

001 001 001 001 001 001 001 001 001 001 11 (cw 4)

Codebook C

In another embodiment of the current invention, same column-wisepermutation as shown in FIG. 4 is applied to Codebook C and Codebook Dis obtained.

1111 1111 1111 1111 1111 1111 1110 1110 (cw1)

1001 1000 1000 1001 1000 1000 1000 1001 (cw 2)

0100 0101 0100 0100 0101 0100 0101 0100 (cw 3)

0010 0010 0011 0010 0010 0011 0011 0011 (cw 4)

Codebook D

In another embodiment of the current invention, when the CCFI has onlythree states, any three codewords in a given codebook (e.g, Codebook A,B, C, D, etc) may be used to carry the CCFI information.

FIGS. 5A and 5B are flowcharts illustrating procedural steps oftransmitting and receiving CCFI according to different embodiments ofthe present invention.

In FIG. 5A, the procedure of generating Codebooks A and C are presented.When the CCFI is transmitted at a transmitter, two-bit CCFI is mapped to3-bit codeword of codebook C1 or C2 as shown in Table 1 at step 201, thethree-bit codeword is repeated for a predetermined times with the numberof the predetermined time being a flooring of quotient └4K/3┘, where Kis the number of resource units at step 203, the resulting bit sequenceis concatenated with the original CCFI bits at step 205 and thus a finalbit sequence is generated and transmitted at transmitting antennas. Atthe receiver side, the receiving antennas receive the transmittedresulting bit sequence from the transmitter at step 211, a demodulatorof the receiver demodulates the received bit sequence at step 213, andthe receiver achieves the information carried by CCFI at step 215 andthus the achieved information carried by the CCFI is utilized by thereceiver.

In FIG. 5B, the procedure of generating Codebooks B and D are presented.When the CCFI is transmitted at a transmitter, two-bit CCFI is mapped tothree-bit codeword of codebook C1 or C2 as shown in Table 1 at step 301,the three-bit codeword is repeated for a predetermined times with thenumber of the predetermined time being a quotient of 4K/3 where K is thenumber of resource units at step 303, the resulting bit sequence isconcatenated with the original CCFI bits at step 305 and thus a bitsequence is generated. Here, the bit sequence may be illustrated as cw 4shown in FIG. 4. At step 307, leading K repetitions of the three-bitcodeword as shown in Table 1 in the resulting bit sequence is mapped tothe number of K resource units respectively with one bit of each ofresource units being open, and the remaining K bits of the bit sequenceare separately mapped to the open bit of each of the number of Kresource units at step 309. Step 307 may be illustrated as theintermediate RU#1-RU#8 each having one bit open as shown in theintermediate bit sequence shown in FIG. 4. Step 309 may be illustratedas the final RU#1-#8 each having four bits allocated as shown by theresulting bit sequence shown in FIG. 4. The resulting mapped bitsequences are transmitted by the transmitting antennas. At the receiverside, the receiving antennas receive the transmitted resulting bitsequence from the transmitter at step 311, a demodulator of the receiverdemodulates the received bit sequence at step 313, and the receiverachieves the information carried by CCFI at step 315 and thus theachieved information carried by the CCFI is utilized by the receiver.

Modulator 101 and IFFT 114 of transmitter 100 include microprocessorsbased controller. Demodulator 134 and FFT 130 of receiver 140 includemicroprocessors based controller.

What is claimed is:
 1. A method for receiving a control channel format,the method comprising: receiving a control channel format indicator(CCFI) codeword; demodulating the received CCFI codeword to identify aCCFI corresponding to the received CCFI codeword; and receiving controldata using the identified CCFI, wherein the identified CCFI is one of atleast a first index, a second index, and a third index, and wherein theCCFI codeword was coded by a transmitter by mapping the identified CCFIto the CCFI codeword using a codebook comprising a plurality of 32-bitcodewords, each codeword comprising ten repetitions of a three-bitcomponent codeword c₁c₂c₃ followed by two CCFI bits b₁b₂ associated withthe three-bit component codeword c₁c₂c₃, the plurality of 32-bitcodewords comprising at least “01101101101101101101101101101101”,“10110110110110110110110110110110” and“11011011011011011011011011011011”.
 2. The method of claim 1, whereinthe CCFI is associated with a number of orthogonal frequency divisionmultiplexing (OFDM) symbols used for transmission of control channels ina subframe.
 3. The method of claim 1, further comprising: receivingmodulation symbols modulated by QPSK modulation; and demodulating themodulation symbols to obtain the CCFI codeword.
 4. The method of claim1, wherein the CCFI is one of at least the first index, the secondindex, and the third index corresponding to“01101101101101101101101101101101”, “10110110110110110110110110110110”and “11011011011011011011011011011011”, respectively.
 5. A method fortransmitting a control channel format, the method comprising:determining, by a base station, a control channel format indicator(CCFI); coding the CCFI to a CCFI codeword; and transmitting the CCFIcodeword and control data to one or more subscriber stations based onthe CCFI, wherein the CCFI is one of at least a first index, a secondindex, and a third index, and wherein the CCFI codeword is selected froma codebook for mapping the CCFI to the CCFI codeword, the codebookcomprising a plurality of 32-bit codewords, each codeword comprising tenrepetitions of a three-bit component codeword c₁c₂c₃ followed by twoCCFI bits b₁b₂ associated with the three-bit component codeword c₁c₂c₃,the plurality of 32-bit codewords comprising at least“01101101101101101101101101101101”, “10110110110110110110110110110110”and “11011011011011011011011011011011”.
 6. The method of claim 5,wherein the CCFI is associated with a number of orthogonal frequencydivision multiplexing (OFDM) symbols used for transmission of controlchannels in a subframe.
 7. The method of claim 5, wherein the CCFI isone of at least the first index, the second index, and the third indexcorresponding to “01101101101101101101101101101101”,“10110110110110110110110110110110” and“11011011011011011011011011011011”, respectively.
 8. An apparatus,comprising: a receiver configured to receive a control channel formatindicator (CCFI) codeword, to demodulate the received CCFI codeword toidentify a CCFI corresponding to the received CCFI codeword, and toreceive control data using the identified CCFI; and an antennaconfigured to enable reception of the CCFI codeword and the controldata, wherein the CCFI is one of at least a first index, a second index,and a third index, and wherein the CCFI codeword was coded by atransmitter by mapping the identified CCFI to the CCFI codeword using acodebook comprising a plurality of 32-bit codewords, each codewordcomprising ten repetitions of a three-bit component codeword c₁c₂c₃followed by two CCFI bits b₁b₂ associated with the three-bit componentcodeword c₁c₂c₃, the plurality of 32-bit codewords comprising at least“01101101101101101101101101101101”, “10110110110110110110110110110110”and “11011011011011011011011011011011”.
 9. The apparatus of claim 8,wherein the CCFI is associated with the number of orthogonal frequencydivision multiplexing (OFDM) symbols used for transmission of controlchannels in a subframe.
 10. The apparatus of claim 8, wherein thereceiver is further configured to receive modulation symbols modulatedby QPSK modulation, and demodulate the modulation symbols to obtain theCCFI codeword.
 11. The apparatus of claim 8, wherein the CCFI is one ofat least the first index, the second index, and the third indexcorresponding to “01101101101101101101101101101101”,“10110110110110110110110110110110” and“11011011011011011011011011011011”, respectively.
 12. An apparatus,comprising: a coder configured to determine a control channel formatindicator (CCFI), and to code the CCFI to a CCFI codeword; and an RFamplifier configured to enable transmission of the CCFI codeword and tocontrol data to one or more subscriber stations based on the CCFI,wherein the CCFI is one of at least a first index, a second index, and athird index, and wherein the CCFI codeword is selected from a codebookfor mapping the CCFI to the CCFI codeword, the codebook comprising aplurality of 32-bit codewords, each codeword comprising ten repetitionsof a three-bit component codeword c₁c₂c₃ followed by two CCFI bits b₁b₂associated with the three-bit component codeword c₁c₂c₃, the pluralityof 32-bit codewords comprising at least“01101101101101101101101101101101”, “10110110110110110110110110110110”and “11011011011011011011011011011011”.
 13. The apparatus of claim 12,wherein the CCFI is associated with a number of orthogonal frequencydivision multiplexing (OFDM) symbols used for transmission of controlchannels in a subframe.
 14. The apparatus of claim 12, wherein the CCFIis one of at least the first index, the second index, and the thirdindex corresponding to “01101101101101101101101101101101”,“10110110110110110110110110110110” and“11011011011011011011011011011011”, respectively.